The present invention relates to electric motor drive control apparatuses having a DC/AC converting section that converts a direct current (DC) system voltage to an alternating current (AC) voltage by using a detection angle of a resolver provided for a rotor of an AC electric motor, and supplies the AC voltage to the AC electric motor.
Drive apparatuses having an AC electric motor are sometimes provided with a resolver for accurately detecting the rotational position of a rotor with respect to a stator, in order to accurately control the speed of the AC electric motor. The resolver includes a sensor rotor and a sensor stator, and the sensor rotor is structured so as to rotate integrally with the rotor. Thus, processing an output signal of the resolver to detect the rotational position of the sensor rotor enables the rotational position of the rotor to be detected. The electric motor drive control apparatus converts a DC voltage supplied from a DC power source to an AC voltage by an inverter, based on the rotational position of the rotor detected by the resolver, and the like, and supplies the AC voltage to the AC electric motor, thereby controlling driving of the AC electric motor. More specifically, the electric motor drive control apparatus determines the phase of a current that is applied to the AC electric motor, based on the rotational position of the rotor, and switches switching devices of the inverter according to the determination.
As described above, the phase of the current that is applied to the AC electric motor is determined based on the detection value of the resolver. Thus, if the detection value has an error, the phase of the current that is applied to the AC electric motor becomes different from the phase of a current that should actually be applied to the AC electric motor. This causes problems such as a decrease in output torque of the AC electric motor, and an increase in ripples of electric power that is drawn from the DC power source. Regarding such problems caused by the detection error of the resolver, Japanese Patent Application Publications No. JP-A-2008-76078 and No. JP-A-2008-256486 below describe structures for correcting the detection value of the resolver based on angle correction data. More specifically, Japanese Patent Application Publication No. JP-A-2008-76078 describes a method for improving angle detection accuracy, where a plurality of angle correction data are provided in association with the temperature and the operating time of an equipment provided with a resolver, and the angle detection accuracy is improved by switching among the angle correction data tables according to the temperature and the operating time of the equipment. Japanese Patent Application Publication No. JP-A-2008-256486 describes that a plurality of angle correction data are provided in association with the amount of current that is supplied to an AC electric motor, and an error due to a leakage magnetic flux from the AC electric motor is corrected by correcting a detection value of a resolver by using angle correction data corresponding to a detected current value.